1. Field of the Invention
The present invention relates to objective lens driving apparatus and, more particularly, to an objective lens moving actuator for use with an optical recording and/or reproducing apparatus, such as an optical disc player or the like for reading or writing an information signal by radiating a light beam on an optical disc in which there is recorded an information signal such as an audio signal, a video signal or the like.
2. Description of the Prior Art
In a conventional optical pickup used in an optical disc player, in order for a light beam emitted from a laser light source such as a semiconductor laser or the like to accurately track a recording track of an optical disc rotating at high speed, an objective lens for converging the light beam is displaced in perpendicular bi-axial directions such as the tracking direction and the focusing direction of the recording track by an objective lens driving apparatus known as a "bi-axial actuator". Further, an optical axis of the objective lens must constantly be held at an angle falling in a range of 90.degree. .+-. about 0.1.degree. relative to the signal recording surface of the optical disc. Considering a lens aberration of the objective lens itself, an aberration of other optical parts such as a collimator lens, beam splitter or the like, an inaccuracy of assembly parts such as an optical pickup device or the like, the bi-axial actuator needs to have an angle adjusting mechanism for adjusting two directions of the radial direction (known as a rolling direction) and the tangential direction (known as a pitching direction) in order to hold the objective lens at the above-mentioned angle relative to the optical disc.
FIG. 1 of the accompanying drawings shows an exploded perspective view of a conventional optical pickup device in which a bi-axial actuator is separated. The ordinary arrangement of the bi-axial actuator and the conventional angle adjusting mechanism will be described below (see U.S. Pat. No. 4,766,583).
The bi-axial actuator is generally depicted by reference numeral 1 in FIG. 1, and an objective lens 2 for converging a light beam emitted from a semiconductor laser (not shown) on a signal recording surface of an optical disc (not shown) is supported by a movable member 3 that is molded by a resin molding process. The movable member 3 is resiliently supported to an attaching mount 4 disposed at the rear side of the objective lens 2 by means of a suspension arm 5. The suspension arm 5 is formed of a pair of parallel flat, resin-molded members made of resins excellent in bending fatigue, such as polypropyrene, polyester elastomer or the like, and housed in a concaved recess 3a of the movable member 3 on its side opposite to the objective lens 2.
The suspension arm (only the upper supporting arm member is shown in FIG. 1) 5, the movable member 3 and the attaching mount 4 are coupled with one another by means of thin resilient displacing portions 6 and 7 so that they can be moved in the left and right direction at their central positions. The suspension arm 5 is composed of thin vertical resilient displacing portions 8 and 9 formed near the respective resilient displacing portions 6 and 7 and recess holes 8a and 9a for adjusting a resilient displacing force are formed through resilient displacing portions 8 and 9, respectively.
The attaching mount 4 is secured to a fixed chassis 10 by self-locking pins 11, 11. Rectangular bobbins 12, 12, each having a focusing drive coil 12a and a tracking drive coil 12b mounted on each surface thereof, are unitarily embedded in the left and right sides of the movable member 3. Yokes 13, 13 vertically implanted on the fixed chassis 10 are respectively inserted into the centers of the bobbins 12, 12 and magnets 14, 14 opposed to these yokes 13, 13 are respectively bonded to support members 15, 15 vertically implanted on the fixed chassis 10 in an opposing relation to the focusing drive coil 12a and the tracking drive coil 12b. A rear plate 16 unitarily formed with the chassis 10 is attached to the rear surface of the attaching mount 4 and a flexible printed circuit board (not shown) for connecting the coils is attached to the rear plate 16.
The bi-axial actuator 1 constructed as above moves the movable member 3 in the upper and lower direction by a magnetic action based on the direction of a current flowing through the focusing drive coil 12a and the direction of a magnetic flux of the magnet 14 when a focusing drive current based on a focusing error signal is supplied to the focusing drive coil 12a. Consequently, the movable member 3 resiliently displaces the resilient displacing portions 8 and 9 of the suspension arm 5 to move the objective lens 2 along the optical axis direction thereof, thereby effecting the focusing control.
Further, when a tracking drive current based on a tracking error signal is supplied to the tracking drive coils 12b, a left and right direction drive force occurs in the bobbins 12 due to a magnetic action caused in the direction of the current flowing through the coils 12b and the magnetic flux direction of the magnets 14. Consequently, the movable member 3 with the bobbins 12 resiliently displaces the resilient displacing portion 6 of the suspension arm 5 to move the objective lens 2 in the direction perpendicular to the optical axis, thereby effecting the tracking control.
The bi-axial actuator 1 thus constructed is mounted on an angle adjusting mount 17 by the chassis 10. That is, screws (not shown) are screwed into tapped-holes 17a of the angle adjusting mount 17 through two through-holes 10a (only one through-hole 10a is shown in FIG. 1) bored through the chassis 10 to thereby fix the chassis 10 to the mount 17. The angle adjusting mount 17 has an opening portion 18 formed therethrough at its position corresponding to the objective lens 2 of the bi-axial actuator 1 so as to introduce the laser beam from the objective lens 2 and an escape opening 18a communicated with the opening portion 18 so as to escape the printed circuit board (not shown) coupled to the coils. The periphery of the opening portion 18 projects to the rear surface side to form a spherical portion 19 of a convexed configuration.
The angle adjusting mount 17 having the bi-axial actuator 1 attached thereto is assembled onto a slide base 20 that is formed by a resin mold member. The slide base 20 has a concaved spherical socket 22 of arm configuration having an opening portion 21 formed therethrough at its center and a rack 23 formed on its one side portion that is used to move the slide base 20 along the radius direction of the optical disc in cooperation with a drive motor, not shown. The concaved spherical portion 19 of the angle adjusting mount 17 on which the bi-axial actuator 1 is supported is fitted into the concaved spherical socket 22 of the thus constructed slide base 20. The angle adjusting mount 17 is coupled to the slide base 20 by fastening a hole 17b of the mount 17 and a hole 20a of the slide base 20 with a pin p.sub.1 and by fitting screws w.sub.1, w.sub.2 into two tapped holes 17c, 17d independently formed through the angle adjusting mount 17 by way of holes 20b, 20c from the rear surface of the slide base 20.
The angle adjustment of the angle adjustment mount 17 relative to the slide base 20 will be adjusted as follows, i.e., the adjusting operation of the angle of the objective lens 2 will be described as follows.
When screws W.sub.1 and W.sub.2 are driven in the positive or reverse direction and unscrewed by a tool such as a screw driver or the like from the rear wall of the slide base 20, the angle adjustment mount 17 is brought in slidable contact at its convex spherical portion 19 with the concave spherical cradle 22 about a pin P.sub.1. In addition, the angle of the angle adjustment mount 17 can be adjusted relative to the slide base 20 while the mount 17 is being flexed. Consequently, the objective lens 2 of the bi-axial actuator 1 supported to the angle adjustment mount 17 can be held on the signal recording surface of the optical disc within a range of a set angle.
Since the above-mentioned conventional angle adjustment mechanism for the bi-axial actuator 1 has a laminated structure such that the chassis 10 of the bi-axial actuator 1 is mounted on the angle adjustment mount 17 and this angle adjustment mount 17 is assembled into the slide base 20, the entirety of the optical pickup is unavoidably increased in thickness in the height direction and accordingly, the optical disc player cannot be reduced in thickness satisfactorily. Further, since the conventional optical pickup needs the angle adjustment mount 17, the number of assembly parts is increased. Also, since the convex spherical portion 19 of the angle adjustment mount 17 is worked and the concave spherical socket 22, which is engaged with the convex spherical portion 19, is machined on the slide base 20, the metal molds for molding the angle adjusting mount 17 and the slide base 20 become complicated in structure and made expensive. There is then the problem such that the manufacturing cost of the optical pickup is increased.
Furthermore, since the angle of the angle adjustment mount 17 of the conventional angle adjustment mechanism is adjusted while the convex spherical portion 19 is slid against the concave spherical socket 22 with friction, the angle adjustment motion of the conventional angle adjustment mechanism becomes non-linear so that the angle of the objective lens is difficult to be adjusted with accuracy. In addition, the angle of the objective lens is adjusted by rotating the two screws W.sub.1 and W.sub.2, which becomes cumbersome.